1. Field of the Invention
The present invention relates to a process for removing boron from brines by the use of an organic extraction medium that contains at least one diol having 6 to 20 carbon atoms.
2. Description of the Prior Art
An important amount of the lithium currently produced in the world comes from natural brines produced in salt mines such as the Atacama Salt Mine (Salar de Atacama). These brines generally have a lithium content of 0.05 to 0.2%. The brines also contain large amounts of sodium chloride, potassium, and magnesium as well as sulfates and other minor elements, including boron. Boron is generally contained in these brines as magnesium borate, calcium borate, or lithium borate.
Even though boron is an element of wide industrial application, it has negative effects on the production of lithium and aluminum. For example, one of the predominant current uses of lithium carbonate is in the electrolysis process for obtaining aluminum by means of fused salts. The boron impurities in the lithium carbonate accumulate in the cell until finally the cell is short circuited.
The same occurs in the production of metallic lithium by electrolysis of fused salts. In this case, the boron present in purified lithium chloride, which is obtained from lithium carbonate, is also accumulated in the electrolyte of LiCl-KCl, producing a low efficiency of current and, as a consequence, a considerable decrease in the productivity of the cells.
Because of these problems, it is necessary to remove the boron before the lithium carbonate production process. If boron is not eliminated before the precipitation of lithium carbonate, the boron precipitates together with the lithium carbonate as lithium borate or tetraborate, thereby causing the above-mentioned results.
Generally, the natural brines with lithium and boron content of 0.01 to 0.5% and 0.05 to 0.1%, respectively, are concentrated by means of solar evaporation, thereby sequentially precipitating a series of salts of different composition, depending on the initial composition of the brine. At the end of the evaporation cycle, the brines may contain 4 to 6% lithium and 0.5 to 1.5% boron, which will then require the elimination of the boron for the reasons stated above.
The methods normally utilized for removing boron from such brines comprises precipitation of the boron as boric acid or extraction of the boron with solvents. In the latter methods, the extractants generally utilized are high aliphatic alcohols, such as isooctyl alcohol, or the like.
The literature cites numerous patents that teach the application of organic extractants for boron, be it from natural brines or from industrial brines.
Chilean Patent No. 37,337 by P. M. Brown and D. A. Boryta (assigned to Cyprus Foote Mineral Co.) utilizes fatty alcohols with 6 to 15 carbon atoms in their structure, dissolved in kerosene. Specifically, isooctyl alcohol with a pH of 1 to 2 is used. This technology does not include a method for re-extracting the boron from the charged (boron rich) organic medium.
U.S. Pat. No. 3,855,392 of Dec. 17, 1974, by Falkestad, Loiten, Mejdell, and Torvund, shows a process similar to the one cited previously, wherein high aliphatic alcohol having between 7 and 12 carbon atoms is dissolved in petroleum ether at a pH of 2 to 4. Extraction is effected at a pH of 8 to 10 in water. Mention is made of isooctyl alcohol as the high aliphatic alcohol best suited for the purpose. This particular process is for removing the boron from magnesium brines suitable for producing electrolytic magnesium.
U.S. Pat. No. 4,980,136 of Dec. 25, 1990, by P. Brown and S. Beckerman, describes a process similar to the two mentioned above, which proposes to also utilize high aliphatic alcohols with 6 to 16 carbon atoms in their structure dissolved in Kerosene with a pH of 1 to 2. In this patent document, however, the manner and the reaction used for re-extraction, which are critical for the economic effectiveness of the process, are not specified.
In U.S. Pat. No. 3,111,383 of Nov. 19, 1963, by D. Garrett, it is proposed to utilize polyols as agents for boron extraction, such as phenyl glycols, glycerol, methyl phenol, and naphthols, applied to liquors and diluted solutions of boron in an alkali medium. This method is not applicable to natural brines.
British Patent No. 1,354,444 of May 30, 1974, by Norek Hydro, also proposes an aliphatic alcohol with 7 to 12 carbon atoms in its structure as an extractant agent. 2-ethyl hexanol dissolved in petroleum ether is used, particularly with a pH of 2 to 4, effecting re-extraction in an aqueous medium with a pH of 8 to 10. This technology is specifically for extracting boron from brines or from solutions with a relatively high content of magnesium, in the absence of lithium.
In U.S. Pat. No. 3,839,222 of Oct. 1, 1974, by E. Grannen, it is proposed to utilize isoamyl alcohol mixed with salicylic acid as an extractant, dissolved in an organic solvent such as a light fraction of petroleum. The results shown, however, do not indicate a very efficient extraction of boron.
In U.S. Pat. No. 3,424,563 of the year 1969, by Grinstead, it is proposed to utilize diols, organic compounds possessing two OH groups in their molecule as opposed to alcohols which have only one OH group, dissolved in an alkali-ammonia salt. The diols recommended are catecols containing 7 to 20 atoms. The alkali-ammonia salt has 12 to 30 atoms in its structure. The re-extraction is carried out in an acidic medium at 20 to 60.degree. C. This type of extractant is very expensive, has a relatively low stability, and is not suitable as an industrial agent.
U.S. Pat. No. 2,969,225 of Jan. 24, 1961, by D. Garret, shows a process wherein the boron is removed from natural brines by utilizing aliphatic diols in a triol solvent. The triols have 6 to 16 carbon atoms in their molecules. Importantly, the solvent used is not specified. Re-extraction is effected in an acidic aqueous medium such as 2 normal of sulfuric acid. These conditions appear excessively energetic for the extractant, since they can oxidize the diol, thereby degrading it.
U.S. Pat. No. 3,493,349 of Feb. 3, 1970, by Schiappa, Place, Hudson and Grinstead, shows the utilization of diols for the extraction of boron from natural or synthetic brines containing magnesium chloride. Among the extracting diols proposed are water-insoluble b-aliphatic diols with 6 to 20 carbon atoms in their molecule, at a pH of 1.6 to 5.0. It is mentioned that the stripping must be performed at a basic pH, without specifying the conditions or reactants required.